Layered models top-down querying of normal logic programs

Luís Moniz Pereira, Alexandre Miguel Pinto

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

11 Citations (Scopus)


For practical applications, the use of top-down query-driven proof-procedures is essential for an efficient use and computation of answers using Logic Programs as knowledge bases. Additionally, abductive reasoning on demand is intrinsically a top-down search method. A query-solving engine is thus highly desirable. The current standard 2-valued semantics for Normal Logic Programs (NLPs), the Stable Models (SMs) semantics, does not allow for top-down query-solving because it does not enjoy the relevance property - and moreover, it does not guarantee the existence of a model for every NLP. To overcome these current limitations we introduce here a new 2-valued semantics for NLPs-the Layered Models semantics - which conservatively extends the SMs, enjoys relevance and guarantees model existence among other useful properties. Moreover, for existential query answering there is no need to compute total models, but just the partial models that sustain the answer to the query, or one might simply know a model one exists without producing it; relevance ensures these can be extended to total models. A first implementation of a query-solving engine based on this new semantics is presented and described here. It uses the XSB-Prolog engine and its XASP interface to Smodels, thereby providing a useful tool built as a hybrid of the two systems and taking advantage of the best of each. Conclusions and further work end the paper.

Original languageEnglish
Title of host publicationPractical Aspects of Declarative Languages
Subtitle of host publication11th International Symposium, PADL 2009, Savannah, GA, USA, January 19-20, 2009. Proceedings
EditorsAndy Gill, Terrance Swift
Place of PublicationBerlin
Number of pages15
ISBN (Electronic)978-3-540-92995-6
ISBN (Print)3540929940, 978-3-540-92994-9
Publication statusPublished - 2009
Event11th International Symposium on Practical Aspects of Declarative Languages, PADL 2009 - Savannah, GA, United States
Duration: 19 Jan 200920 Jan 2009

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume5418 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference11th International Symposium on Practical Aspects of Declarative Languages, PADL 2009
Country/TerritoryUnited States
CitySavannah, GA


  • Relevance
  • Semantics
  • Smodels


Dive into the research topics of 'Layered models top-down querying of normal logic programs'. Together they form a unique fingerprint.

Cite this